The present invention relates to blends of rubber-modified copolymers of isopropenyl aromatic monomers such as alpha-methylstyrene and vinyl aromatic monomers such as styrene.
Impact resistant polymeric compositions are well known in the prior art. Particularly well known are those impact resistant polymeric compositions comprising a rubber-reinforcing polymer dispersed in a rigid phase polymeric composition. Exemplary of such impact resistant polymers are those containing styrene acrylonitrile and a reinforcing rubber. These impact resistant compositions comprising styrene acrylonitrile and a reinforcing rubber are known in the art as ABS or ABS-type compositions.
These impact resistant compositions can be prepared in a variety of ways. One method of preparation is to polymerize styrene and acrylonitrile in the presence of rubber, for example, by a mass or bulk polymerization process, to obtain a rubber-reinforced styrene/acrylonitrile resin. Alternatively, said polymers can be produced by blending heat-plasticized grafted reinforcing rubber with heat-plasticized styrene acrylonitrile resins.
While the incorporation of rubber-reinforcing polymers into nonrubber-containing polymer compositions is generally effective to improve impact strength, it is quite often accompanied by a reduction in other properties, such as heat distortion temperature. Thus, it would be advantageous if rubber-modified polymeric compositions were available which exhibited not only desired levels of impact resistance but at the same time displayed desirably high heat distortion values with lesser negative effect on other properties, such as gloss, thermal stability and hardness.